Meteosat

METEOSAT or Météosat ( Meteosat in English) is a meteorological satellite family of carried out under control of work of the European space agency (ESA). They are satellites Géostationnaire S, i.e. they always preserve the same position compared to the Ground, and thus allow the observation uninterrupted precise zone of the sphere.

The Météosat satellites send regularly on Earth of many digital images of terrestrial surface and other data which allow the meteorologists, starting from the observations of Anticyclone S, atmospheric depressions, cloudy masses (etc), to work out the weather reports. These data are also essential to anticipate certain devastating weather phenomena such as the hurricane S, Tempête S; and for the follow-up of the evolution of the Climate of planet.

History

The Météosat program belongs to the world system of observation of the atmosphere, set up by the World Meteorological Organization in the middle of the years 1970. It includes/understands five satellites équi-distributed on the Geostationary orbit, all in the plan of the equator, with the following longitudinal positions:

0 degree, Meridian of Greenwich (vertical of the Gulf of the Gabon): Meteosat, carried out by Europe;
75°W: an American satellite GOES-E;
135°W: another American satellite GOES-W;
140°E: a Japanese satellite;
74°E: an Indian satellite. It should be noted that to the origin of the program, this orbital position had been allotted to the USSR. In front of the deficiency of this country required a satellite to the “Western standards”, it is India which saw itself D-allotting the position.

The satellites Météosat , of first generation, were produced in the Space center of Cannes Mandelieu by a consortium created for this purpose: COSMOS, under control of work of aerospatiale. At the beginning of the program, in 1970, the chief of program was Roger Imbert.

The first satellite, Météosat 1 , was launched the November 23rd 1977.

In 1995, EUMETSAT (European organization for the exploitation of meteorological satellites) officially took the responsability for the financing and the exploitation of the Météosat satellites and the diffusion of their data. It launched the continuation of the program:

See also: Météosat second generation

Today, three Météosat satellites of first generation are still in exploitation: Météosat 5 observes the India; Météosat 6 and Météosat 7 observe the Europe.

It should be noted that this program is the first large (even only) operational application program of the ESA ensuring a continuity of service thanks to satellite of replacements (those of first generation, then those of second generation). With same, since the Eighties, a Redundancy of satellites in orbit : there are always two of them on the meridian line of Greenwich, ready to continue the service, if one breaks down.

In 2007, one celebrates the 30 years of the program!

Operation

Météosat functions like a Scanner. During its rotations, with 100 turns per minute, around its main axis, a Radiomètre analyzes “line-images” of terrestrial surface, which are converted into 2.500 point-images digitized (pixels). They are transmitted, almost in real-time, towards the control center of the satellites (ESOC) located at Darmstadt, Germany. Since its altitude of 36.000 km, the Earth is seen under an angle of 18 degrees, that is to say one twentieth rotation of the satellite. During the remainder of rotation, the radiometer is rocked to the top of the equivalent of a “line-image”. Following rotation makes it possible to take a contiguous new line of the preceding one. It is at the end of 2.500 turns (either 25 minutes) that 2.500 lines were analyzed, thus providing a matrix of 6.250.000 pixels, and this in various wavebands. During a few minutes, the radiometer is quickly rocked downwards, loan for new a scan. The scans are started automatically at the round hours H and H+30 minutes. One thus obtains 48 scans per day (this is valid for Météosat of first generation; rates were doubled on those of second generation).

The raw data are treated with the control center, then transmitted to various users, of which the European Center of weather forecasting in the medium term (CEPMMT) located at Reading (Berkshire, the U.K.) in charge of the development of the mathematical model of atmospheric circulation, but also towards the national offices of meteorology - of which the Center of Space Meteorology (CMS, to see external bond) Météo France - for their own treatments and supplies of images reconstituted with the various television channels and their newspapers weather.

Image quality

The studies of the quality of the images were undertaken with CNES, in very first place by Jacques Breton and Jean-Pierre Antikidis. After the beginning of the construction of the satellites at aerospatiale in Cannes, a more complete team was installation, including/understanding representatives of the two principal industrialists: Matra for Radiometer and aerospatiale for the satellite. After characterization of the defects being able to cause losses of quality, studies of software making it possible to correct them were undertaken, as from 1975. They led to software of correction which was established with ESOC in Darmstadt, in time for the launching of the first satellite in November 1977. At the beginning of the program, the person in charge “image quality” was Guy Lebègue.

It is necessary to note an implication in these studies, in the years 1970, of Laboratory ARMINES of the École des Mines of Paris, all lately established on the all being born technopolis from Sophia-Antipolis. Its development team of software of space image processing was implemented under the direction of Michel Albuisson.

Calibration of the radiometer on the Moon

Little time after the launching of the first satellite, an anomaly appeared on the mechanism of calibration of the way Infrarouge. Indeed, to gauge perfectly the values of infra-red information, representative of the temperatures observed on the Earth, the radiometer is equipped with a “black body” of removable reference. It is the mechanism of displacement which posed concern.

After dialog with all the teams working on this problem, the solution came from the the Moon!

Indeed, our natural satellite is visible from time to time in edge of the images of the Earth taken by Meteosat, and this several times per month. The idea came from Guy Lebègue, person in charge of image quality of the satellites, with which it associated Astronome S of the observatory of CERGA, in Grasse, equipped with telescopes observing the Moon, including in infra-red. It was enough to enregister of the typical images of the Moon, the “seas” in particular whose temperature was to be well-known, of the American astronauts there being already walked.

Alas, all the literature of NASA, consulted, did not comprise this information. It is thus a theoretical and practical study, coordinated by Guy Lebègue, which was implemented in this beginning 1978 with a modeling of the temperature of the “seas” according to solar illuminations and checking by the measurements taken by the telescopes of the CERGA by one of the astronomers, Jean Gay. In April, a model ready, was transmitted to ESOC for programming of the software of calibration, under the direction of Jean Ber.

This original and new operation was worth a contribution to the 29th congress of which was held with Dubrovnik in September of the same year.

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